A catheter attached to a balloon (for example, a balloon catheter) can be employed in a biological organ dilating method of placing a stent in a stenosis of the blood vessel or body cavity (for example, a biological lumen such as biliary duct, esophagus, trachea, urethra or the like) to secure a body cavity space. A catheter attached to a balloon can be employed in the therapy of ischemic heart disease or the urethral catheterization of a patient who has difficulty in urination. A method can be employed which includes expanding an affected area (stenosis) of the coronary artery or the urethral catheterization by passing from the urethral opening to the bladder. Such a balloon catheter includes a body shaft, an inflatable and deflatable balloon attached to the vicinity of the distal end portion of the shaft, and a hub attached to the base of the shaft.
The inflatable and deflatable balloon catheter can have characteristics including trackability (following performance of the balloon against a tortuous blood vessel or body cavity), capability of passage into a stenosis such as of a blood vessel, dilatability of a stenosis such as of a calcified blood vessel or the like. It can be desirable for the catheter balloon to have flexibility, thinning capability and high strength.
For such a balloon, materials can be used such as polyethylene terephthalate, polyolefins, polyamides and the like. Since polyethylene terephthalate is a high-strength material, a thinned balloon can be formed therefrom in order to increase trackability. There is a concern that when contacted with a calculus or a calcified affected part, the thinned balloon may be formed with pinholes, resulting in the breakage of the balloon in a body cavity or blood vessel. On the other hand, when the balloon is formed excessively thick, the flexibility and trackability of the balloon can be impaired although press capacity is ensured.
Polyolefins can be heat-sealed to the shaft and show flexibility and thus can be processed. Nevertheless, they can be relatively low in pressure resistance and can have such a tendency that the balloon diameter greatly changes relative to a change in balloon inflating pressure. Therefore, when a high pressure is exerted on the balloon, the balloon can sharply become enlarged, with the concern that a body cavity may be overdilated, or elongation along the axis may cause a normal body cavity or blood vessel to be dilated.
Nylons or polyamides have substantially intermediate properties between polyethylene terephthalate and polyolefins. If they are formed to be thinned, characteristics with respect to the pressure capacity and pinholes may be undesirable. If formed to be thick, the resulting balloon can become hard and may not have satisfactory trackability.
Techniques of forming a balloon by laminating a plurality of materials in the form of layers are disclosed, for example, in Japanese Patent Laid-open No. Hei 3-205064 and Japanese Patent Laid-open No. Hei 9-164191.
In Japanese Patent Laid-open No. Hei 3-205064, there is proposed a technique wherein a multi-layered balloon including a layer containing polyethylene terephthalate and a layer containing a polyolefin is described. A hydrophilic polymer may be coated on an outer surface of the balloon. It is stated that such a balloon is consequently excellent in lubricity, breaking strength, limited radial expansion, bondability with a shaft, and reinforcing characteristics including rupture characteristics.
In Japanese Patent Laid-open No. Hei 9-164191, there is described a balloon of a multi-layered structure having a base layer made of a high-strength polymer, and a covering layer formed on at least one surface of the base layer and made of a flexible polymer that is more flexible than the high-strength polymer. It is disclosed that the flexible polymer can have an elongation at breakage close to the high-strength polymer and be more flexible than the high-strength polymer. It is disclosed that when a high-strength polymer and a flexible polymer that has an elongation at breakage close to that of the high-strength polymer and is more flexible than the high-strength polymer are thus chosen to provide a multi-layered balloon, the flexible polymer fully functions to improve the strength of the balloon as a whole to obtain a flexible balloon of high strength. It is stated that such a balloon can be formed thicker than a balloon made of a single high-strength polymer layer, so that pinholes are reduced.